ML19309G452

Summarizes Technical Issues Involved in Interrelationships Between SSE & OBE in Determination & Application to Design

ML19309G452
Person / Time
Issue date:	10/08/1976
From:	Minogue R NRC OFFICE OF STANDARDS DEVELOPMENT
To:	Mason NRC COMMISSION (OCM)
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ML19309G451	List: ML19309G450 ML19309G452 ML19309G453 ML19309G454
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SECY-79-300, NUDOCS 8005060327
Download: ML19309G452 (19)

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UNITED STATES 3

NUCLEAR RECULATORY COMMISS!ON j

WASHINGTCN, D. C. 2:!55

., - y F.

4

'% V OCT 8 M

j

!O C W C 1 FCR: C:I::missioner Mason I

FRCM:

Rcbert B. Minogue, Director Office of Standards Develegnent TERU:

Executive Director for Operations SUBE:

'E: REU.TICESHIP SEriEEN SAFE SINiN EARECUAKES AND OPERATING 3 ASIS EArcECCAKES In respctse to ycur recuest this mecrandtra su:=arires for your information ard dat of de other Cm=issioners the technical issues involved in the interrelati:nship between the safe shutdown ea'rthcuake (SSE) and operating basis ear $q.:ake (CEE) in their determination and application to design.

4 NRC regulations (A pendix A to Part 100) identiff two levels of earthgaake severity to be applied to reactor seisnic design. These are c=M ed the safe shutd:wn earthq2ake (SSE) and the cperating basis earthquake (CEE).

These eardq;akes can be and are regarded and defined as either geologic events or as engineering design regairements. These t:eo perspractives are often difficult to relate to one another. Both points of view are explicit in A;;endix A.

Viewed ceclecically, the SSE is the mest severe earthq2ake which can affect :ne s2.:e.

The CBE is the n:est severe earthecake which is reasonably likely t: cccur during t'.e egerating lifetime of the plant.

Appe.di: A defines in detail the elsents of the geologic and seismolcgic investigaticn of prepcsed sites. Ceterministic precedures are given to establish de safe shutdown earthcuake. These precedures require censideratior of (a) de seis=olcgy of the regicn in which the site is located, (b) the regicasl and 1ccal geclegy, and (c) the nature of the materials underlying the site. If the structural geology of an area is underst cd, A;;endix A procedures for detencining the SSE usually have the effect of placing greater ec;i. asis en structural geology than on historic seismicity, largely because of the II:sitad histcric record.

Centnet:

Robert 3. Minegue 443-4914 Enclosure "F"

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13 00T 8 W6 v

1 Cc=.'issicner Masca he inte.t of these precefures is to identify the max!=t:m earthecake whi.h cr. affect the sita. dere is, of ccurse, scme probability of exceeding the SSI. 2.is p cblem is because of the uncertainties arising f:c: cur limited understanding of the fregaency and severity of large scale earth?ca'te phenc:ena and the limitaticas of geologic and geophysical inv,estigaticns, :ader than lack of validity of the concept of a limiting eard ? ake. In a sense, then, the likelihcod of exceeding the SSE is a measce of de state-cf-the-art of geolccic and seismologic understanding; it p:= ably is en the c:dar of perhaps 10-6 in any given year for any site, but wi:h a very wide error band.

de cperati.~g basis earthgaake, although an infrecuent and major earthgaake, is a =uch =cre liksly gecicgic event. The recurrence interval frecuently censidered applicable te de CSE is in the range of 300 to 1,000 years.

Alth: ugh in engineering practice the CSE is usually established as a fracticn cf de SSE, in nr.y parts of the ccentry there is a sufficient record cf histcric seis:ic events to prcvide a basis for a p:cbabilistic assesste.t of the CSI if these events are censidered in light of the regicnal st:uct= al gaclegy.

Appendix A does not 7:escribe specific geologic precedures for establishing the CBE (aldcugh ic dces specify a minimum level). An ANSI standard

• has been drafted describing a methed of p:cbabilistic assessment of the CEE. Prchabiliscic analysis es used for establishing the CBE for the Koshkencng bclear Pcwer Plant. We application for a ccnstruction permit has been :eviewed and a=epted by ACP.S.

21s a=:cach of e.m levels of severity of a natural phenomenon is not unicue"tc earthecakes. 2.ere is a good analcgy between the cencept of the'SSE and CSE"r.d dat of the Prcbable P.aximt:s Flecd (P!7) and Standard Project Ilced (SPF) used by the U. S. Ar=y Corps of Engineers (and NEC).

ne level cf likeli'ced of these two flood d% 'wge levels is sdstantially the sate 2s de SSE and CEE, respectively.

Viewed as a clied ec.encineerine desien, the design basis for the SSE is spec:.-.e: :n Appenc:.x A to assure tnat the plant design adecuately l

protects de pdlic health and safety in the event of an extrece eardgaake.

The CBE is established as the most severe earthcuake following which i

de pla.t can safely be cperated withcut special inspections.

I

• " Guidelines fc: Cetermining the vibratory Ground Motic.n Cor the resign Eards;2ke fc Muclear Facilities", ANS 2.1 Working Grcup Draft, Jr.uary 1,1976.

I Enclosure "F"

.o Cerraissioner Mason -

4 Ergineering ccdes and design practice apply these two earthcuake levels differently. Category I structures, systems, and cc=ponents*, must maintain their safety function for earthquake levels up to and including the SSE.

'lhat is, although the plant, as a pcwer generating facility, may be severely damaged in this extrace event, it must go through the earthcuake without undue hazard to the public ard folicwing the earthgake the reactor must be capable of being shut dcwn and kept in a safe shutdown condition.

On the other hand, the engineering design cbjective with the CBE is that the plant is capable of heing safe in operation after experiencirs an event less than or ecual to the GE.

As an exa=ple of hcw these events are applied to design, in use of the ASE Eoiler and Press =e Vessel Code, the SSE is normally applied as i

a Faulted Cc:x!itica, meaning that stress levels allcwed by the Code which would result in permanent general deformation are prmitted except when defcaatica wculd lead to less of safety functicn. Cn the other ha.nd the GE is censidered as an tyset Condition or Design cerxiition in applicatic of the Ccde and is used in conjunction with lower allowable stress levels at which no general deformation wculd cccur. In addition to differences of allcwahle stresses, there are other differences in design analysis methods in the appl %ation of Faulted and C;: set Conditions. Many seismic I

designers see the 53E as being the basic seismic design basis with the GE playing more the :cle of a cross-check basic using different analysis procedures and different limits to assure the adecuacy of the margin provided by the SSE design over a wide range. Viewed frem this persp:ctive the GE is mere of an ergineering safety factor applied to design analysis rather % being seen as a seismic event.

To prcrida such a safety factor, Appendix A to Part 100 centains the statemant. that the "Maxist:s vibratory g:cund acceleration of the.Cperating l

3ases Earcquakes shall be at least ene-half the maximira vibratory ground acceler*cn of the Safe Shutdeun Earthcuake." 'Ihis is a scmewhat arbitrary relatierWp which assures that the stresses asscciated with design lead j

l cc:Wi.2:icns plus the GE loading en systems essential to safe operation will nc result in general yielding of the materials _(i.e. will remain in the elastic regime). -

Cn the other hand, if viewed as a seismic event the acceleration associated with the CEE may rarse f:cm as low as 1/10 the SSE to as high as 80 or l

90%.

In parts of the ccuntry where the structural geology is not well urx!erstood, current practice would lead to GE's typically about 1/2 l

the SSE; that is, :cughly one Intensity unit icwer.

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• Defined and listed in Regulatory Guide 1.29, "Seismir. :esign Classification' 1

Enclosure "F"

J CCT 8 86 Ccrcaissicner Mascn The shaki g asscciated with actual earthgakes is a very canplex vibratory motien with wide variations in fregency centent, amplitude, ard duration depending en the ty:e of initiating crustal =cveent and the transmission of de =ctica thrcugh de earth. Normal engineering practice is to define the vibratcry nctica 1 put as it affects the facility with a cc:posite resp::se s:ect:=. based en a nuater of eardgake records. Usually this res==..se spectrum is :sfuced to a time-motion record (a synthatic seis=ogram) for applica: ion to design. Bis engineering definition of vibratory untien irput is gaite cc plex and contains a number of elcents of arbitrary conservatism. A grcup of Regulatory Guides

• has been issued which provides a ec:plete definition of the vibratory motion input for reactor facilities.

9.e only distinctica heressn the S5E and the CBE in the application of these res ense spectra to design is a scaling by the canparative acceleraticns.

tere are a n=her of specific issues ar4 problem areas that are related to the deter-i atics and application of these two events which are identified a-4 hriafly described helcw. Attachment I is a detailed staff analysis discussing de stject at greater le.mth, prepared with the assistance of the X??. Divisics of 5ite Safety and Envircc: ental Analysis.

1.

Is the CEE a safa:7-related event in the strictest sense?

t Many pecple do nct regard the CEE as a safety-related event. Cesign of the plant to widsta-d the 53E withcut undue public hazard is felt to meet the safety need. Se decisien whether or not to centinue operatien of the plant afta: an eardgake is seen as a decision of the utility.

.If an erdgake shculd cccur, the safety of the plant for centinued i

operation could be es-*ished by a suitable, possibly cuite extensive,

,, inspection p cgram widcut regiring design to an CEE level. As originally published for c:==ent Apperdix A reflected this perspective by maki q the estehl% en: of an CBI cptional. Perhaps the best argunent for regarding tha'CEI as a safety-related cuestion is a recognition that in the aft =- th of a major earthgake needs for power would be significant.

Pr%. centinued reac:c: cperation might be a carmunity requirement.

Adother arg=en: scca.imes advanced is that the widespread shaking of the eardgake affects reactor systes in estplex interactive medes which are not easily foreseeable. mis makes it apprcpriate to recuire sa:e letel of general earthecake design within the elastic ressense rarge; but in fact application of CSE design to struct=res, systems, and c=p:nents nc: also ecvered by 55E design is gaite rare.

• Regulate:y Guides 1.60, "Cesign Respense Spectra for Seismic Design of l

Nuclear ?cwer Plants"; 1.61, " Damping Values for Seismic Cesign of l

mcles: ?cvar Plants"; 1.92, "C=:bining F.cdal Ees=enses and Spatial l

Cc:penents in Sais=ic Respense Analysis"; and 1.122, "71ocr Cesign Respense 5:.setra Cevelescent fer Seis ic Design of Flec:-Supported Egi;=ent or Cc=perents".

Enclosure "F" m

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Cccaissioner Mason

-5 OCT 8 8

2.

Shocid the CBE be established as a seismic event or as an emineering safety factor'

?

A widely-held engineering view is that the analysis of a seismic 1 cad in i

the rage of frcm 1/3 to 1/2 the S5E prcvides the best emineering verificatic of seismic design, and that the CBE should be established in this range at a value such that the seismic design is detemined by the SSE, not the CBE, since the CBE is seen as a design check. Note that other ncn-seismic factors cay centrol the design cverall. On the other hard, if detemined probabilistically as a geologic event, the CBE would not necessarily be within this ra.ge, and may or may not detersine seisnic design.

3.

What vibratory motien characteristics shculd be assumed for the CBE?

The c _jle:.:lti-fregency shakirg of an earthquake is nocnally represented for design pt._gses by a highly censervative smoothed respense spectrum.

The same respense spect rm shape is noc: ally used for both the SSE ard CBE design, adjusted cnly as to acceleration. Since the CGE is an eart5.cuzke of Icwer intensity ard likely shorter duration, a less conservative res;cnse spectrus might well be apprcpriate.

4.

Eow should isolated acceleraticn peaks be treated?

It is not unusual in an ea'rtheuake to have a high amplitude acceleration peak of limited duration and little impact en the respense of a ceraplex structure. For exa=ple, such a peak (1.25 g) was measured at the Pacoima Dam in the San Ferna:do earthquake in 1971. Current practice is to base the engineering design en a response spectrum which implicitly assumes sustained shaking (ard in effect disregards isolated peaki ceu on the general engineering censensus that isolated peaks do not have any significant effect cr. structures.

5.

What inspections should he carried out following an earthgake exceeding 4

the r==?

i Apperdix A dees not provide guidance on this matter. It is very difficult before the fact to identify in a generic way exactly what inspection prcgram wculd he appropriate after an earthgake. Ccnversely, folicwing an earthgake cbservable effects on the facility cocid reasonably be expected to indicate the areas recairing inspection and the types of inspection needed. The s*=## pcsition has been that the leiel and extent of inspection 'follcwig an earthgake should be based en observed damage ard a ccmparison between l

the scccched respense spectrum used as a design basis and the respense 5,. un ccrres;x:rding to the motion actually experienced by t.5e facility.

g Enclosure "F" m-

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e,

CCT 3 375 Cc=issicner Mason,

2e actual shaking can be detecuined by seismic inst:t=entation recuired 1

en all = clear pcw: pir.ts to ceasure earthgaake input. An MEI camittee wh' '- dereicped a strdard defining seismic inst:tnentation regairements to ceasce input

• is new well alcng en a standard which defines a basis for assessing "exceeda.ce" of the design respense scectrt:a in a real eient**,

to pr: tide a basis for decisien on level and type of inspection based en the actual facility respense.

v.k Y /$ b'N 4

Ecbert B. Minogue, Director Office of Standards Development At*-a.t:

Ce. ailed Staff Analysis cc: Chai=zn FcWr.

Cs=issione: Gilinskr Ca=issioner Ka=edy" C2-ice of the Secretary

• 23: 513.5, "Eardgaake Instru=entatien Criteria for 22 clear Pcwer Plants",

e.dcrsed r4 amplified in Regulatory Guide 1.12, "Instrunentaticn for

• Eardq;akas".

• • R3: N543 (M3 2.10), " Guidelines for Eetrieval, Review, Processing, ard r/aluatica fc: 2ecc:ds Cbtained fran Seissic Inst:=entation".'

Enclosure "F"

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r ATIACP.ENT I STAFF P2PCRT CN SASES FOR SEIICTION CF i

SA?Z SEL.EGm EA EOUAE (SSE'S) AI,'D OPEF.ATING BASIS F__'EHO*AK?.S (CEI'S) IJ1D TEE FID."_ICESEIP EEriEEN TEE SiO I.

_?l5E I SIT %._' CN WITE PIGAF.D TO TEE BASES. FCR SEESCTICN OF SSE The Safe Shutdcwn Eardkuake (SSE) is that earthcuake which is based en an svaluation of the' maxi:m::1 earthgeake potential in the region of de nuclear pcwer plant site. The etaluation is based on a cc..sideratica of the regional and 1ccal geology and seismology and en the s:ecific characteristics of the material on which the power plant will be 1ccated.

For sale =i:n cf de SEE, Part 100 Appendix A describes two distinct l

gecl:gical/se e-1:;ical situaticas within which sa.et/ cat different i

p:ccedres are reg ired f:r determining the SSE: (1) ',. hen the seismicity can he :Cz:ed t: ge:1:gic structures a.d/or capable faults and (2) when sei-inity ra-.ct he reizted to geologic structures and/cr capable faults.

A.

Situation Cne: When Eartheda'<e Generating Structure Can Be 2.

'"ne first situatien, in which seismicity can be related to

_geclegic stru :=es anf/or capable faults, is more typical cf de w=c-=- r-4ted States, which is a region of cm:tplex gec1%. a-d high seismicity. The following four steps represent current s%'" pracadure for establishing maximum SSE acceleration 4

4" --8s situa.ics:

1.

Cet= '.atien cf tectenic structures. An assessment of the ear nTe.a.<e n'. story of tne area 2.n wnich a nuclear pcwer plant will be located is made. Tnis assessment includes the

.regaency of occurrence, and the maximum earthquake of recc:5. Tac:enic structures in the area that have associated seied:ity are identified. By definition tectenic structures are larga scale dislocations er distortions of the earth's crust and may or may not enccmpass capable faults. For example, the San Mdreas fault zone of California and the Cinci:_.ati Arch are both censidered to he tectenic structures.

Cne represents a rupture of the earth's crust, and the ot'.e:

a large flexure.

If the maximum historic ez:thqdake eccurs en a tactenic structure either near or upcn which the power plant will be situated, the earthcuake is treated as though it t ck place at the prescsed power plant site.

D*"lD *D N Y 5\\

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,J,IL Enclosure "F" i

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i A""J.C5DTf I.

By means of historic records Ce:er-instion o' Cacable Faults.

an: geolcgical invest:.gations, capable faults vnich cculd 2.

Table I fras c:.7ceivably affect the site are identified.

Sectica I7 of Appendix A to 10 CFR 100 presents a minks fault lers:h versus distance fec= site, for censideration of the,

fault in establishing the SSE. For capable faults, the These characteristics characteristics of the fault cust be kncwn.

are determined frca historic records and by geologic investigation they include the legth of the fault, a=ount and nature of displacacant on the fault, physical properties of rock and soil asscciated with the fault, and infocuation on past movecents of the fault.

I Since a fault dces not Esca=iratien of maxi um earthcuake.

3.

usua__.y rup:ure along its entire length, an effective rupture Current staff practice is to leng h zus: he established.

ass =e that apprcximately 40% of the total fault lergth will be 1:icivsf in any single event.

Given this rupture length, a: earthgeake c:cgnitude is the fault. a:pirical relationships between detac hed fc:

rupture legth, earthcuake magnitude, and displacenent haveThe relati bee.. develcped and are used for this purpose.

de eloped en AEC centract by Ecnilla ani Buchanan (1970) purpose is cost widely used, although others (Alger=issa f-

' ' d e anf Ambraseys ard Tchalenko (1953)) are sanetimes employed (ipi-)

This 22xt:= earthgaake has always been larger than the maxin:.r:

histcric earthgaake associated with the fault; howeeer, the

=axin= '..istoric earthgaake would be used if it were the larger of he : t.

The maximca De:e:- 'a=tica of raxi:mra acceleration at site.

es: _. gear.e Intensity is assc:ec to occur on the portion 4.

cf -he fault or tectonic structure cicsest to the plant site.

Given the earthcuake and the distance to the site, the acceleratica at the site is determined using attenuatica Cther relationships develcped by Schnabel and Seed (1973).

-e = 'anships (Hofnann (1974), Ecuaner (1965), tenevan (1973))

are also s=etimes used. The largest acceleration resulting at the site frc= the earthcuakes on the rarious capable faults is then used as the maximum vibratory acceleratica for the Appendix A regaires that this acceleration be at least SSE.

one-tenth the acceleration of gravity (0.lg).

Enclosure

. a.

.- AT;"m.E:72 I 3.

Situaticn Two: When the Cause of Historic Earthcuakes Cannct ce Reiarec to Kncwn Geolecic S Itc ures 2.e secc.-4 situation, in which seis:7.icity cannot be related to geolcgic structure and/or capable f Aults, is typical of the eastern United States, where it ha9 gsneral'y not yet been possible t: relate seiAity to tectonic r,tructures or capable faults in many areas.

In this case, tectonic previnces are used in the establishment of the SSE. The fellcwing steps present current staff precedure in this situation.

1.

Cere:-i.ati= of tectonic province. A tectonic province is (as cef =ec in Apperclx A) a region of the North American i

cen_inent characteri::ed by a relative censistency of the geclepic strue: ural features. There is no definitive i

ga.ermy accepted identification of such provinces in the-

\\-

Unitsi States. Several province maps exist (by. King (1969),

Eardley (1962), Hadley-Cevine (1974)) ard are used for general guidance, but the basic determination of such a province, if recuired, is made on a case-by-case basis.

2.

Daterinatica of maxistra earthcuake. Since in the second EEua::.cn we are concerned wirn a region in which seismicity f

is net related to known gecicgic structures, the maximt:n hisecric earthcuake of the region is treated as though it cculd anywhere in the tectenic prevince (i.e., at the plant oc=:

site). Geological evidence, a high level of seismicity or a shcrt historical recc d, may dictate the use of an eardcua'<a intensity greater than that of the maximt:n historic earthquake of the tectenic province.

Nhen an adjacent tectonic province has experienced an earthgak greater '+=n those of the tectenic prc7ince in which the pcwer plant is to be located, the maximtra recorded earthquake of the adjacent prevince is treated as though it occurred en the border of the two provinces at the point closest to the pcwer plan: site. The effect of such an earthquake en the plant site is de: ermined as described belcw.

3.

Dete=inaticn of caximra acceleraticn at site.

Most historic ear:ncua.<es in ene eastern Unitec States are recorded in terms of v.cdified Mercalli intensity (Im), a.d the maxistra earthquak for the site is also specified in Is.

A maxim = acceleration is derived frca this intensity.

A number of correlations of acceleration c:.d intensity have been develeped by varicus authcrities.

Cescaly used is the relaticnship developed by Trifunac and Brady (1975).- A relatienship frca Neu:aann (1954) is also sc:etires used.

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Enclosure "F" I

i I ATD.CETC I i

For =ui== earhtg.:akes pres =ed to occur at the border of adjacen: tectonic provinces, the intensity of that eardguake is cc:: erted to a Richter magnitude usi~;

relatic= ships developed by P.ichter (1958) or Nuttli (1974).

Given this =agnitude, the maxin=2 acceleration is calculated in de sa e =r.ner as for earthcuakes asscciated with known -

faults, using the same attenuation relatic= ships.

In de case of the Charlesten SC 1886 and New Madrid MO 1311-1312 eardguakes, the recorded intensity contours are used to dete=ine the intensity at the site, ard the site acceleratica is dete=2ined f:ca relationships such as Triftmac a-3 3:ady (1975) or Netnann (1954).

II. 55I CI5IGN ?I5 C:52 5PECTRA Tc d=" e de 55I recisely for engineering design purposes, the maximin heri=ntal g::u-i. =--M =-=" ion associated with the SSE for a given c clem: p: w_: pir.: size is established by the applicant and approved by de EC. Afte egreeing en the maxhtn ground acceleration for a given site, Regulate Guide 1.60, " resign Response Spectra for. Seismic y

Design cf Nuclea: Icwer Plants," scaled to the SSE acceleration, is nocally used f:: es-=-lishirg the free field grcund vibratory motion associated with de 55I for the site. The applicant also has the optien of using site-depa-is.t design respctse spectra in place of those given in Eng1.12:::7 Guide 1.63.

It is.cinted c= in Regulatory Guide 1.60 that the acceptable design respense spec. = p::ceire for nuclear gewer plants is a procedure devel. ped as a :ssult of two statistical studies of response spectra j

f:c: pas eard71.atas. A st= mary of the tuo studies and the recc---elei design precedure is centained in the paper entitled "seis=ic resig: 5pectra f:: Muclear Power Plants" by Nathan M. Newnark, Jchn A. 31=e and Kanuar K. Kapur ( ASCI, Journal of the Power Division, Nc7e=:er 1971). In a study by John A. Elt=e, a total of 33 different

.ea-d=a.:e race:ds were censidered, with the peak ground accelerations fer. :sa ea-tr.:2kes ranging frcm 0.11g to 0.51g. A total of 23 records

= *-"'y by Nathan M. Necark, with the caxintn ground v.-s

. u.2 4.-

acceleratiens in -he horizontal direction ranging frca 0.03g to 1.25g.

1 Respense spectra were calculated for each record for varying degrees of d__ :ing and cean spectra uere derived frc:2 statistical analyses. The resi.:s of the two studies were cc:bined a-d a single spect:t=t was rec =: e-ded f:r design pur;cses, usi : = ean Mus one. standard deriat; ion as de d. esi n scect:ts crebability le. vel.

2-l i

D.# " D fP 0 M F

I Enclosure "F" Q

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5-ATG.CE:mzt I It can he seen therefore that the characterivtics of the actual e=---- -ke re:::ds used by Blt:ne and New: ark, such as their fregency c:.te.t a.d de duration of their metiens, are-inherent in the design spectra fc=d in ?.egulatory Guide 1.60.

Since a ncher of ccnditices a a e=elcped in ?.e ulat:::v. Guide 1.60 r the detelog ent of s:cothed si_e depe.-den: spectra f :n a single eerdgake record would be less l

censanative bece-e= b ccvers caly cne corditien.

l I

It is i.,~rtant to egiusize that the peak ground accelerations of the ear.h:; takes used in de alce ard Newnark studies are maxist:2 motions cbsened indecen:ient:;_gf the duration of c:cund =% king _at those levels.

TM.tr du es a degree df conservatism into design spectra, since iti

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l is well estabi'=b=d in eardgake engineering that the most damaging c::=d ccti:ns are typica.71v. those leiels of motion (frecuentIy of lower d 4.ude t' an de peaks) that are maintained for lenger periods of time.

!!I. ~;?ISTE 5;...."_ 03 '=nn RIG.UD 7J TEE BASES EUR SELECTION GF TEE CSE "ne Cpera ir; 3 asis Ia $..:1ke, as defined in 10 CFR Part 100, Appendix A, is ea eare:; ne -t.ich, censidering the regicnal and 1ccal geolcgy ard sei=:1:=7 a-d spacific chnicteristics of local subsurface material, I

c:uld reascr='-t y ':e expe:ted to affect the plant site durir-the operati.~a s

life :f de pir.:.

It is that earthgake which p:cduces the vibratory g cund :: tion f:: /..i:h dose featres of the nuclear gewer plant necessiry for c=:inued cpera:ica without undue risk to the health and safety of the pd'ic are designed to renain functional.

Se 21:1 = value cf de acceleration lavel for the CSE is currentiv

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specified in Appendin A to 10 CFR Part 100 as at ieast one-half the ac-=' =-= ' n da: ermined for the SSE and this is tha value nc=a=11y spec' " ='

r~ site _s.not. in highly seisnic are_as, th_%-eequiss; tent is.cen n:111 ; in he sele.cti.o.n of CEE.

In these areas, ear ake a

acc,,s a icns un.,:n..._can reasonsoly_ be expectec_ to cccur in the life of the plant will usually be less than one-half the SSE acceleration.

FC: si as in hi bly seismic regicns (mainly in the western United l

S '-* = e = c=ple description of the CBE is develcped. Geolcgic strunture tect nic previnces with which historical earth:;uake I

ca-e ' =

"1'

a 1.-i:y has her. asscciated are censidered as pcssible source mechanisms.

- '-i-"y calculatics such as those described by Algec issen and Perkins I

(197!, 1976) can be used to help estimate the a: eleration letel that can reascnably be expected to affect the plant dring its operating life f

(app::ni.ately forty years). 'Ihis acceleration may be greater than one.al the 33I acceleration for s=e sites.

l i

e Enclosure "F" a-

=

/

s 6-ATD.C.5m I To define de GE precisely for engineering design stirposes, the same res;cnse spectrun as that for the SSI is used, scaled only as to

-.1.-=tien.

i O.e pni'.:sephy behird es'=hlishing the CBE to be not less than one-hald SSI is as follcws:

1.

O.a stress letal in 'the safety-related struct=es, systems, and c_

nents is allcwed to reach yield level when the plant is subjected t= a SSE in c=bination with other applicable loeds, provided the necessary safety fu.cticas are maintained. For the CBE, all structures, rysts:s, a.-3 c=;cnents necessary for centinued eseration without

'.. lee risk te the health and safety of the public are designed to

z- = 3. f=ctienzl a-d well within elastic limits when subjected to the GI in c=ti.ation with nor=al operating loads. The usual range of a2 vanle el" '- ---==s is frcct 0.45 to 0.6 of the yield stress.

'~.ne ch:i=e of -l.e CEE to be ene-half SSE is consistent with the i

rati: cf de y*=' * ---==s (allcwed for SSE) to the allcwable elastic s ress (s'leved fr GI).

2.

gpe-lin A

: C CTO. Part 100 requires that the nuclear pcwer' plant be shut d: n if de vibratory around motion exceeds that of the CEE.

C.is regi enent 1-di:ates 'the advisability of an GE which is large encugh so that during a strcng earthquake all the nuclear power pir._s in a large gecgraphical area are not shut do n and the public lefn viticut sis:=ic ;cwer.

(It shed.d be n:ted tna: another a:plicatica of the CBE arises when seismic effects z:e c:nsida:ed in cc2ination with other natural phenomena. For exa=ple, in dete=hing de design basis for certain structures of the ultimata heat sink, de GI is censidered in cc bination with waterflow based en severe his Orical events in the region of the structure. 'Ihis applicaticn of the GI is basi:s'ly not gecane to the issues of SSE/CSE interrelationship discr.ssed in this pape:F.

o IV.

=._. r m._ _/. _ _CN 1. nz: REGARD 'IO ENGL. r e.IFG DESIG1 !ECCU:GT '

05E; ICE SII5:CC OISIGi CF.:L.WIS SCT.UECTED TO SSE AND CSS O.e a--* '-=A diagrz: cutlines the dcct: tented seismic design methodelarf bei.:g. sed t: day in the engineering design of nuclear power plants relatite :: the SSI and CSE.

~

7 A;:endin A to 10 CFE Part 100 requires that vibratory motions of the 35I and '3E be defined by respcase spectra of the Loc =dation level l

cf de ;1r.t. 9.ese spectra are cbtained by decenvolving the,three-I dire:t :n=1 spect a specified in Regulatery Guide 1.60, which are q

Enclosure "F" m

l

s L-

• a

. ATD.CSMEm I free field spectra.

Fc: these free field spectra ?.egulat::7 Guide 1.60 sp* == twe hcriz:ntal spectra having the same a:plification factor and r erti:21 spe:t:_: hrring amplificatien factors which rarse frca ne sa.e :: 1/3 cf de a plification factor used for the hori ental spectra.

- - = p::cass of de::=civing, time histeries campatible with the free fia~d spe =a are generated. Engineering analizis of the site is perfected c fi-2 tne c cca:ible bedrock motions. Rese bedreck moticas are used in s:i' s=ue:re ' interaction to find the plant foundation motions, ne f:=dati:n leiel teti:ns (represanted by spectra or ti: e-histories) are in =:. tsad in de s :::: ural mcdel of the nuclear power plant to fird streases and displa: scents in various ele:ents of the plant and the ficor desig. response sp:-:=a t r be used sdsegaently in the design of floor-s___:::-f evt.i;:en rd c=penents. Sc=etimes structure-to-structure in: ara:t:.:n z.alysis rust he perfc=ed if two or more structures are in c':se p:::inity f ea:. Other. This anslysis may further mcdify the f:t-da i:n Icel iasi:n input into a nuclear power plant structure.

_: _.__., _~_... _ u.m-S __ CT_..m.

C=,r :=. S~:.

._..__s..

u v

..m

-=-= '-

pan:i:y of data for usa in determining the magnitude of de ee:rg:ske associated with a given fault lersth.

cercuin types cf ezr.n?.:2ke scurce mechr. isms (such as overdrust faults s.d rev=-*= "i i.g resulting f:ca cw.gessional failures) t generail. hE e higher effective stresses across the fault, laafi.? :: g: eater ene gy releases ard thus greater magnitudes t'.an 9:i.i he expected for a strike-slip or normal dic.-slio_

fault. T e e is ssne feeline chat the mere frecuentiv used

.i empirica'. ela-icnships are dar.inated by data for the refe:se-tyce '*"'-, leading to u-duly censervative magnitudes for other "zul s.

_'.ese e _pi-ical relationships contain an additional censervative

- + = = Aus t: M"'-ulties in determining the rupture le.gths of 51:lts ass: cia:ed with past eardq akes. Since portiens of the fault nay he h=ied beneath landslides or a deep alltriial soil

.ryer, es_=.stes of rupture ler.g$s associated with past earthgaakas

-=-4 -- -= =---ter than the actual rupture lengths.

The ra'aticnships dev-leped using dese rupture lengths will then

-- W -- -

9 censervative (larga) earthq:ake magnitudes for we'l-es:2:lia'Riault length a..5 pcstulated rupture length.

i 3.

In establishing the maximum acceleration for a site, there are differences of opinion ame..g seismolcgy experts regarding de taxi.-_-. pcssible near-field (clesa to the fault) acceleratien dat can be generated. tat is, there is scme physical upper limit cn near-field acceleratica, regardless of earthqcake me:nitude: the disagreement is en de value for this upper limit.

l

3

, ATIACEMm I C.

Very high isolated paak acceleraticas here been ceasured but ara not used in scaling and applying Fagulatory Guide 1.60 design spectra. These maximum accelerations are usually of short du atica and do not have t.me to build up dacaging energy.

near-geak accelerations maintained for 1cngar durations will be more damaging. Tne duration of strong notion is particularly significant for design stresses near the yield point (as is the case wi,th the SSE).

D.

Cetermination of tectonic provinces is a point of contention between d e staff and industry. In general, staff practice is to use relatively la_;ge tectonic crevinces to ensure conservative design. Ecwcrier, there is a great deal of tas_=ical arg=ent frca industry to use s= aller tectonic pr:ri. css.

E.

te_acinatien of taximum acceleration frca intensity creates difficulties in that intensity is a subjective measure of grourd

-i:n.

Alsc, direct infor:ation abcut the duration of strong n:-ion is les: h.en using intensity as a measure. Tais is a difficult problem since al= cst all earthcuake data for the eastern United States is in terms of Mcdified Mercalli intensity.

VI.

D? Z-r ISSCES hTIE ESPECT TO ELATICNSHIP SETWEEN COE 74G SSE A.

Tre CBE ca. he censidered to be not safety-related and

-Jarefera appropriately chosen by tha applicant as a matter cf econctic judgatent.

In such a case the guiding factor f:r the applicanc to choose a cartain g-leiel for the CBE wculd te de cost f shutting dcun and restarticg the plant afger an

'=r eccurs. If the acplicant chooses too low a letel for the

.I, he =ight incur heavy costs of shutting down and restarting he plant several times during the life of the plant.

Further, if the plant generally has an inadecuate seWe design basis ha arf incur extensive costs due to earthgaake damage to power generatica and transmission eqai;=ent. (As an example damage to utility systems in the San Fernando earthgaake a cunted to ahcut 5100,000,000).

i F.egulatorf Guide 1.12 specifies that varicus seismic instruments be used to ascertain whether the CSS has been exceeded during an earthgaake. When instrumentation show that the peak i

acceleration er the respense spectra experienced at the foundatica of the centainment building er in the free field excaed the CBE acceleration lezel or ressense spectra, the plant is,regaired to be shut down pending permissien to res=e operaticn. To l

detemine whether or not the plant can safely resume operaticns, Enclosure "F" qm m

y L

. e J\\\\..e.m 1 A tru.m 1

. ATIACE:E r I visual field inspectica of safety-related itees, which may include rcriest:cetive testing if need is indicated, is impleanted a-3 the ceasured ressenses frca both the peak-re:Ordi.g 2-3 st:crg-motion acceleregraphs are ccrpared with

_hese ass =ei in the design. Ccnsiderable cost and time is hv:17e5 in this prccess of inspection ard verification, which includes such itscs as (1) inspecting the piping for any mcvenent c: :chbi.g, (2T inspecting the structures and ecui;mmt for a:nc=al displacement, (3) reviewing the recorded data on plant c;erating paraneters for any ahner:al cperation of eg2ip:nent dring eten:, and (4) cc:: paring the recorded respenses sit:

2 Se design hasis. To cc= pare the responses, the earthgaake data mus he re=iered f::= the instru::ents, digitized, and used in the ccgut

'*y technical specifications of the licensees are r.alyses. Cs used te acc=glish the inspectica and ccmparison of the ressenses.

cf the staff feel that the GE should be established c-a - =--= - =

S.

based en p:dabilistic metheds, rather than being specified as Bis cculd be dene by checsing an earthqmke cf -Je SSE.

="-=-#--

'--= ral to c'ctain a sufficiently small prcbability of r=~r--=--=

exc=#=--= d::ing the c;erating life of the plant, and mcdifying er eli=inati.g the requirement that the CBE be at least one-half One difficulty with this approach is in how te select the SSI.

an app: pria:e recurrence interial. Also, there is very little earthgea':s data for the eastern United States, creating problems in det=-ini.; the earthgaake seterity for a given r. :urrence O.ere is sete feeling that the historic records for Sterval.

north - eri:a are too short for use in predicting geologic phenane-Se s-= =' has a wide range of cpinions on how such an appccach been cases for which an CBE less

'snculd he used. There have ena-rLi SSE has been accepted by the staff as the earthgaake

1. - =,

W.ich ec213 reascnably be expected to affect the plant during its i

l

~t :pera:ing life.

l Sc=e fe-:1 Sat the minimum CBE should be set semetere in the It is their

ance cf cne-:hird to ene-fot:th of the SSE.

'-=" with an GE egaal to one-half of the SSE, the cenien'#--

4desi-. Of =r.y c=sponents in a nuclear gewer plant is gcverned by lead e

'-4-= Hens irriclving the CSE rather than by conbinations While reducing the CBE/SSE ratio might Y_inich i.clude the SSE.n sc=e cases, reverse the situation, in othe s

P =- -==M y centrols the design are the choices of load factors, The Cez is on1 leading c=binations, ard allowable stressas used.

ne of :he loadings but in many cases the cceination of ncnseicnf To overcare lends. as the centrolling effect on the design.

his pr:blem, the lead cccbination gaestiens and allcwable s_resses wculd have to be retised to give different weightings to the 1 cads involved. Differences of opinion exist within the staff on whether er not this should be dene.

" I **

D**D

• ]D p[lY @

. a Juu2UAL i

oo

r; ATIACE EZr I -

i i

VII.

n'PC.:*N I55 TIES WIS EE SEI5MIC CESIG:r tESCCCLCGY 1

A.

Pagulatory Guido 1.60 is based cnly on limited data.

Chere is reca for: impreisent in the shape and a:plitude i

of the free field design res;cnse spectra as a function of =agnitude and distance.

Pegulatory Guide 1.61, which gives the da= ping valtas to be used 3.

in the seisuic analysis of the nuclear power plants is based on limited test data ard engineeric.g judgement. Pecm for im=:ciment also exists here, because a slight difference.

in da= ping values can make a substantial difference in the resulting stresses in various caaponents of the plant.

C.

Esculatory Guide 1.60 specifies that the same amplification fa: tors he used for the two horizontal spectra, and gives a separate set of amplification factors for the vertical spectrtra.

tere is sc e feeling that the amplification factors for the seccrd horirental spctrt:m and the vertical spectrt:s can be less than these given in Regulatorf Guide 1.60.

Se shape of the spectra as given in Regulatory Guide 1.60 is D.

act suitable for soil licuification analysis, according to so e visus. A site-catpatible spectrus is more apprcpriate for thase analyses.

E.

Soil is a nonlinear material when subjected to the dynamic otion of earthquakes. At present cost of the soil-structures interactica analyses and site analyses for decenvolving the ti=e-histcry =otions are based on the elastic (linear) properties cf the scil. tere must be a substantial improvement in the staterof-t'.e-art before nonlinear analyses for soils can be incor; crated into the design methodology.

F.

In carrying out the structure-to-structure Interaction analyses, the major problet eaccuntered is the same as in soil-structure interaction analyses, i.e., the elastic rather than inelastic properties of the soil are used in the analyses.

. Dere are two usual kinds of analyses which are performed on structures subjected to earthquake motions: (1) response spectrum analysis and (2) time-history analysis.

The major question raised ahcut.the res;cnse spectrum technique is how to ca bine the modal respcase and the effects of three cm,Anents of earthquakes.

Regulatory Guide 1.92 specifies procedures based on the present state-of-the-art.

Enclosure "F" T ' ],&

t q

.o

. ~

ATIACSEZE I I" -# ~ 'istory techniq2e is used and a simultanecus analysis of de dree directions is perfor ed, the problems of medal c:tbi.ation and three cw.ecne.ts of earthgaakes are eliminated.

Ecwever, the precedure regaires a cc::.puter with very large mencry capacity, theref:re it is not being widely used at present.

R.

Beg"' story Guide 1.122 specifies precedures to broaden and smccth de flecr respense spectra.

The guide also prevides the precedure to c

'-ine. the three ficor response spectra for a given direction.

The questicas raised about the guide include the ascunt of broadening and the precedure to cc=bine the three spectra for a given direction. The guide is based on the present state-cf-de-art and can be improved in the future.

VI12. :. ::: ESC ~S 10 * -

=-- 200, A pendi: A, " Seismic an:1 Geolcgic Siting Criteria for gu.-t e

_. ;,- m.-- a ReTalat::I Gcide I.12, "I.strumentation for Earthgaakes" Regula::ry Guide 1.60., ".2esign Response Spectra for Seisnic Design of Nuclear Pcwer Plan 2" Regulat:-- Guide 1.51, " Camping Values for Seis[ sic Eesign of Nuclear y

Pcwer Plants" Regula=-I Guide 1.92, "C=bining Medal Res_ronses and Spatial Cc=sonents in Seisni: Res; case Analysis" Regula=:f 3 cide 1.'", "Flcor Cesign Respense Spectra Development for Seis=ir resign cf ?lec: S' :perted Egai; ment or Ccmpenents" S. T. Alge=issen, " Studies in Seismicity and F2.rthcuake Damage Statisti=," U. S. Ccast ard Geodetic Survey (1969)

S. T. Alpe=*=a =" D. M. Perkins, "Technicues for Seisnic Zoning:

1.

GE.e al C nside sti ns and Paraceters," Proceedings of the Inter.ar.:nal C: fere.ce on Microzcnatica, Seattle (1972)

5. T. Alge=issen a-i D. M. Perkins, "A Prebabilistic Estimate of Menimum i

A::ala a-i:n in 200k in de Centiguous United States," U. S. Geolcgical S2.: ey ;en File Report 75-416 (1976)

N. H. A :rzseys and J. Tchalenko, "Cccunentation of Faulting Asscciated vi_n Ezr :q:akes," Part I, Dept. of; Civil Enginsering, Imperial College cf 3:lence, Lc.-den (1958)

~

h j

j

, ATD.CEir?r I M. G. Sonilla and J. M. Ecchanan, " Interim Report c$ !!orldwida Historic Surface Faulting," U. S. Geological Survey Cpen File Report (1970)

N. C. Conovan, "A Statistical Evaluation of Strong Motion Data Including the Fe: ruary 9,1971 San Fernando Earthg.:ake," Prcceedires, Fifth World r

'Ccnfarance on Ear & quake Engineering, Ecme (1973)

A. J. Eardley, "Structu'ral Geolcgy of lierth America," Earper & Row (1962)

R. B. Ho'-".n, " State-of-the-Art for Assessing Earthplake Eazards in the United States, Report 3, Factors in the Specification of. Grourd Motion for Cesign Ear $ quakes in California," Misce 11cneous Paper S-73-1, U. S..:sf Engineers Waterways Experiment Station (1974) i G. W. Ecusner, " Intensity of Earthquake G:ctr.d Shaking near the causative Fault," Precaedings, Third World Conference on Earthquake Engineering, liaw ::aaland (1965)

P. 5. Eing, "?.e Tec::nics of North America - A Discussion to Acccmpany Tectrair Map cf :cr-h Anarica Scale 1:5,000,000," Professional Paper 628, U. S. Geolcgical Servey (1969)

F.1:ec:ar., " Earth? 2ke Intensity ard Related Grouni Phtion,"

University of Washi.;t:n Press (1954)

O. W. Mu:-li, " Mein'- 'a "ecurrenca "=' =' den for Central Mississippi Valley Eart= cakes," En'letin Seismolegical scelety of America, Vol. 64 (1974) l C. F. Ri:h:er, "F.la '.tary Seisacicgy," Fres=an & Co., San Francisco (1958)

P. B. Scr abel and E. 3. Seed, " Accelerations in 2cck for Earthcuakes in the Western United States," Bulletin Jeiemological Society cf America, 7cl. 63 (1973)

M.D. Wi'r.ac a.d A. G. Brady, "Cn the Ccerelatica of Seismic Intansity Scales Zith Peaks of Recorded Grcund Motica," Eulletin Seismological Sccietf of A. erica, Vol. 65 (1975) g gy IoaJ

. dlL o

9

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